Personal care products typically are made with a top sheet material (also referred to as a cover sheet or liner) an absorbent core and a liquid impervious back sheet. Some may also have a surge layer or other specialized layers between the top sheet and absorbent core. Absorption of fluid, comfort and avoidance of leakage are the functions desired.
An ideal feminine care product, for example, would have no leakage and deliver comfort and discretion to the user. Current feminine care products may have relatively high leakage and thus offer only modest protection to the consumer. A leak is rather arbitrarily defined in the art, however, as menstrual discharge that stains, contacts or discolors the underwear or body. All leakage is categorized by three key causes: fluid does not absorb into the product, fluid is absorbed into the product but subsequently leaves it, or fluid never contacts the product.
The specific reasons for leakage may be expressed further in terms of definitive mechanisms. A product, for instance, may not have suitable space for absorption due to localized saturation or low contact area. The product may not have a suitable driving force for absorption because the structure does not have the right balance of permeability and capillarity. The interfiber spaces may be partially full of fluid. Fluid may contact the pad and run-off. The fluid may be too viscous or the pores or interfiber spaces are not large enough to allow fluid to pass through to the subjacent layer.
Various attempts have been defined to reduce product leakage. Wings were developed to cover the underwear and thus reduce leakage by reducing the area of the underwear that could be soiled or contacted. Other products have embossing lines or shaping lines which cause the pad to fold in a predefined manner to concentrate fluid loading in a specific area or to increase the contact area of the pad with the body. Still others have attempted to reduce leakage by focusing on side or edge leakage presumably caused by compression of the pad by the legs thereby reducing the contact area of the target zone. These product designs have focused on keeping absorbed fluid away from the edges of the product and directing it toward the center. In many cases this is a function not only of the assembly of materials of different size and shape but also their ability to conform to and contact the body in predefined ways.
In all cases, the material systems and their concentration in a specific product design dramatically impact leakage. In the field of material systems design, leakage is a function of materials shaping and conformability as well as intake, distribution, retention and transfer.
Intake includes the initial absorption of fluid into a dry product as well as the continued uptake of that fluid into the absorbent structure. Development of superior intake systems requires an understanding of environmental conditions including the nature of the fluid and its discharge. Developing functional intake structures requires an understanding of material characteristics and their interaction with the fluid as components and systems of components including interfaces and product design. Product design includes the arrangement and geometric design of material components and their interaction with the body and fluid.
Initial intake of menstrual fluid into an absorbent article is also a function of the characteristics of the liner or topsheet material and the upper absorbent layer.
Intake of menstrual fluid into these materials is a function of the material characteristics including the ratio of void volume to fiber surface area, fiber orientation and fiber surface wettability. These intrinsic material characteristics specifically define the more familiar material properties of permeability, capillarity and fiber wettability which can be calculated and measured by techniques well known in the art. Regardless of the characteristics of the liner, a suitable intermediate layer and absorbent core must be matched to it to permit fluid communication and transfer and thus good fluid intake.
There remains a need for a personal care product that is able to contain the body exudates in such a way as to keep the wearer comfortable and protected from fluid being expressed back onto the wearer or the undergarments.